Process and device for loading fibers with calcium carbonate

ABSTRACT

For a process and an apparatus for loading fibers contained in a pulp suspension with calcium carbonate, a calcium oxide and/or a medium containing calcium hydroxide is fed to the pulp suspension, and the so treated pulp suspension is further charged in several reactors with pure carbon dioxide or a medium containing carbon dioxide. The reactors can be connected in series and/or in parallel.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention concerns a process for loading fibers contained ina pulp suspension with calcium carbonate.

[0003] 2. Description of the Related Art

[0004] Pulp suspensions of the above-mentioned type are used especiallyin paper and cardboard manufacture. The sparing use of raw materialresources, due especially to economical and ecological concerns, isreflected in the paper production industry by the use of paper web withlower basis weights, as well as by the partial replacement of pulp withfilling materials. If lower cost raw materials are used, the paperquality should at least be maintained. Among other things, the endproduct's strength, visual characteristics, and processability play keyroles in this challenge.

SUMMARY OF THE INVENTION

[0005] The present invention relates to a process and apparatus forloading fibers with calcium carbonate, especially in terms of optimumreaction balance, optimum reaction speed and optimum flexibility ofproduction output.

[0006] The invention comprises, in one form thereof, a process of fiberloading that includes adding calcium oxide and/or a medium containingcalcium hydroxide to a pulp suspension, and then charging the pulpsuspension in several reactors with pure carbon dioxide or a mediumcontaining carbon dioxide. Upon the addition of calcium oxide and/or amedium containing calcium hydroxide to the pulp, an exothermic chemicalreaction takes place, the calcium hydroxide being added in liquid form(lime milk). By using lime milk, the water settled in or on the pulpsuspension's fibrous material is not necessarily required to start andcontinue the chemical reaction.

[0007] Because of this development, the chemical process, which is thebasis of the loading, is split into several small processes, therebypermitting an optimum reaction balance, an optimum reaction speed, andan optimum flexibility of production output to be achieved. This use ofseveral small processes enables a targeted and optimal testing ofpartial reactions, switching on and off of partial reactors and avariation of the operating parameters in the partial reactors.

[0008] On loading the fibers, calcium carbonate is imbedded into thewetted fiber surfaces by adding calcium oxide and/or calcium hydroxideto the wet fibrous material. Thereby, at least part of this calciumcompound can associate with the water of the pulp mass. The so treatedfibrous material is then charged with the pure carbon dioxide or themedium containing carbon dioxide.

[0009] As a result, the term “wetted fiber surface” can include allwetted surfaces of the individual fibers. Consequently, the fibersbecome loaded with calcium carbonate both on their outer surfaces and ontheir insides (lumen).

[0010] Accordingly, the fibers are loaded with the filler materialcalcium carbonate, whereby the accumulation on the wetted surfaces takesplace by a so-called “Fiber Load™” process, as described in U.S. Pat.No. 5,223,090. In this “Fiber Loading™” process, the carbon dioxidereacts with the calcium hydroxide to form water and calcium carbonate.

[0011] For one suitable arrangement of the process in conformity withthe invention, at least one section of the reactor is connected inseries. Several smaller reaction volumes are created from one largereaction volume, so that the reaction speed is increased and,correspondingly, the contact surfaces of the reactants are enlarged.Furthermore, in an advantageous manner, (crystallization-) processes canbe achieved in a targeted fashion and the parameters for an optimalreaction can be matched.

[0012] With a further advantageous arrangement, at least one section ofthe reactors is connected in parallel. In addition the above-mentionedadvantages, this arrangement also allows for optimum adaptability of theproduction output. It is also of advantage, in parallel-connectedreactors, to produce calcium carbonate with different crystal types and,preferably, to mix these on termination of the production process. Thismixing allows an optimal composition of the product.

[0013] In certain cases, a combination of series- andparallel-connection of the reactors are of benefit. In this way, theparallel section can be matched to the required production range.

[0014] In other respects, the loading of fibers with calcium carbonateis as described in U.S. Pat. No. 5,223,090. The content of that patentis hereby incorporated by reference herein.

[0015] The apparatus embodying the invention essentially includesseveral reactors, in which the pulp suspension, mixed with calcium oxideand/or calcium hydroxide, can be charged with pure carbon dioxide or amedium containing carbon dioxide.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The above-mentioned and other features and advantages of thisinvention, and the manner of attaining them, will become more apparentand the invention will be better understood by reference to thefollowing description of an embodiment of the invention taken inconjunction with the accompanying drawing, wherein:

[0017]FIG. 1 is a schematic illustration of an embodiment of the fiberloading apparatus of the present invention.

[0018] The exemplification set out herein illustrates one preferredembodiment of the invention, in one form, and such exemplification isnot to be construed as limiting the scope of the invention in anymanner.

DETAILED DESCRIPTION OF THE INVENTION

[0019]FIG. 1 shows in schematic an apparatus 10 for loading fibers,contained in a pulp suspension, with calcium carbonate (CaCO₃).Correspondingly, apparatus 10 serves to add the calcium carbonate to thewetted fiber surfaces of the fibrous material. In this way, this loadingof the fibers, especially in accordance with the aforementioned “FiberLoading™” process, takes place.

[0020] Apparatus 10 includes several reactors 12, in which the pulpsuspension, mixed with calcium oxide (CaO) and/or calcium hydroxide(Ca(OH)₂) can be charged by pure carbon dioxide (CO₂) or by a mediumcontaining carbon dioxide (CO₂). Moreover, reactors 12, can be connectedin series or parallel. It is possible to have a series arrangement, aparallel arrangement, or a combination arrangement of series andparallel for reactors 12. Also, with parallel-connected reactors 12, itis possible to produce calcium carbonate with different types of crystaland to mix these, preferably on termination of the respective productionprocess.

[0021] Before, after and/or within the group of reactors 12, a fluffer14 can be fitted, in which the fibrous material can be dissociated fromthe pulp suspension, with the aim to so increase the specific surfacearea of the fibrous material. Thereby, susceptibility for the reactionproducts on the fibrous material surface is optimized. Consequently,there is a continuing improvement in the homogenization, and the “FiberLoading™” process is optimized.

[0022] With this design example, first fluffer 14 is fitted betweenrefiner 16 and reactor 12. Alternatively, or additionally, it is alsopossible to fit such a fluffer 14 between at least one reactor 12 andtank 18. With this example, another refiner 20 follows tank 18. Afterwhich, the loaded pulp suspension is fed to paper machine PM.

[0023] Via a pressure-reducing device (not shown), the pre-treatedfibrous material can then be fed, continuously or discontinuously, toone or more material feeds (not shown) of paper machine PM for furtherpreparation. The pressure-reducing device can be a valve, especially arotary valve, an enclosed worm-wheel, a sectioned sluice, a tank, anexpansion device (e.g., such as a nozzle or turbine), and/or anothersimilar device.

[0024] For example, by use of apparatus 10, calcium carbonate (CaCO₃)can be added to the wetted fiber surfaces of the pulp. This loading ofthe fibers can then take place according to the aforementioned “FiberLoading™” process.

[0025] Consequently, the calcium oxide and/or the medium containingcalcium hydroxide (slaked lime) can be so added to the fibrous materialsuch that at least part of it can associate with the water present inthe fibrous material, i.e. between the fibers, in the hollow fibers, andin their walls. As a result, the following chemical reaction takesplace:

CaO+H₂O lime slaking→Ca(OH)₂ slaked lime

[0026] In an appropriate reactor, the fibrous material is then socharged with carbon dioxide (CO₂) that calcium carbonate (CaCO₃) isextensively added to the wetted fiber surfaces. As a result, thefollowing chemical reaction takes place:

“Fiber Loading”: Ca(OH)₂+CO₂→CaCO₃+H₂O (Calcium carbonate+water)

[0027] Independent of the kind of apparatus in question, variousconditions and measures, either individually or in an optionalcombination, are of benefit with regard to further optimization of theloading process.

[0028] The pH value of the pulp suspension can be measured to monitor orregulate the chemical reaction. In doing so, the pH value can be setwithin a range from about 5.5 to about 10.5.

[0029] The ash content of the pulp suspension can be regulated within arange from about 1% to about 70%.

[0030] The carbon dioxide can be introduced in a gaseous form. Thetemperature of the fed carbon dioxide is practically controlled within arange from about −10° C. to about 250° C.

[0031] As an example, a pressure regulation in the approximate rangefrom 0.1 bar to 20 bar is possible.

[0032] Optical properties can be used as indicators for the regulationof the chemical reaction. For example, these properties can bebrightness, luminosity, opacity, color, and light dispersioncoefficient.

[0033] Fundamentally, it is also possible to use the pH value, the ashcomponent, and/or the calcium carbonate (CaCO₃) component as controlparameters for controlling the chemical reaction. In the areasidentified with “VD” in FIG. 1, dilution (H₂O) is also possible.

[0034] Also the following conditions and measures, individually or in anoptional combination, can provide further optimization of the fiberloading process:

[0035] Feed of pulp:

[0036] Regulation of volume and mass flow;

[0037] Temperature control within a range from about 5° C. to about 95°C.;

[0038] Density control in the range from about 15% to about 40%,preferably from about 20% to about 25%;

[0039] pH value controllable from about 10 to about 13;

[0040] Calcium carbonate (CaCO) in the reactor:

[0041] Crystal types: rhombohedral, scalar, rosette, spherical,needle-shaped, prism-shaped, aragonitic, plate-shaped, GCC, and similarcrystal structures;

[0042] Reaction under about 0.1 bar to about 20 bar;

[0043] Temperature from about −10° C. to about 250° C.;

[0044] Dwell time from about 0.1 minute to about 1 hour;

[0045] Fluffing:

[0046] Serves to increase the specific surface area;

[0047] Can be fitted before, after and/or within a reactor(s);

[0048] Dissociation width from about 0.1 mm to about 100 mm, preferablyadjustable;

[0049] Energy input within a range from 0.1 kWh/t to 200 kWh/t,preferably 0.5 kWh/t to 9 kWh/t;

[0050] Refining:

[0051] before, after and/or within a reactor(s) or the “Fiber Loading™”process; Pressure vessel or reactor (*)/dwell pulper after reactor (**)

[0052] (*) Crystal types: rhombohedral, scalar, rosette, spherical,needle-shaped, prism-shaped, aragonitic, plate-shaped, GCC and similarcrystal structures;

[0053] (*) Reaction under about 0.1 bar to about 20 bar;

[0054] (**) Temperature within a range from about −10° C. to about 250°C.;

[0055] (*) pH value controllable from about 5.5 to about 10.5;

[0056] (**) Material density about 0.1% to about 15%;

[0057] (**) CO₂ addition;

[0058] (**) Dwell time; and

[0059] CaCO₃ component in the pulp:

[0060] With an underlying percentage by mass of about 1% to about 70% ofthe filling material, about 1% to about 60% filling material beingdeposited onto the fibers and the remaining being free FLPCC™ (FiberLoaded Precipitated Calcium Carbonate) in the suspension.

[0061] While this invention has been described as having a preferreddesign, the present invention can be further modified within the spiritand scope of this disclosure. This application is therefore intended tocover any variations, uses, or adaptations of the invention using itsgeneral principles. Further, this application is intended to cover suchdepartures from the present disclosure as come within known or customarypractice in the art to which this invention pertains and which fallwithin the limits of the appended claims.

What is claimed is:
 1. A process for loading calcium carbonate intofibers contained in a pulp suspension, the process comprising the stepsof: providing a pulp suspension comprised of fibers; providing acalcium-rich medium, said calcium-rich medium being comprised of atleast one of calcium oxide and calcium hydroxide; adding saidcalcium-rich medium to said pulp suspension to form a calcium-treatedpulp suspension; providing a plurality of reactors, each reactor beingfluidly coupled to a source of a carbon-dioxide medium, saidcarbon-dioxide medium being one of pure carbon dioxide and a mediumcontaining carbon dioxide; and charging said calcium-treated pulpsuspension and said carbon-dioxide medium into at least one reactor topromote a chemical reaction to form calcium carbonate and thereby loadsaid fibers with said calcium carbonate.
 2. The process of claim 1,wherein said plurality of reactors includes at least one section ofreactors, said at least one section of reactors being connected inseries.
 3. The process of claim 1, wherein said plurality of reactorsincludes at least one section of reactors, said at least one section ofreactors being connected in parallel.
 4. The process of claim 3,comprising the further steps of: producing a different crystalline formof calcium carbonate in each of said parallel-connected reactors; andmixing together said different crystalline forms of calcium carbonate.5. The process of claim 4, wherein said mixing step occurs after theproduction of all of said different crystalline forms of calciumcarbonate being formed is completed.
 6. The process of claim 1, whereinsaid plurality of reactors includes a combination of parallel-connectedreactors and series-connected reactors.
 7. The process of claim 1,wherein each of said pulp suspension and said calcium-treated pulpsuspension have a pH associated therewith, the process including thefurther steps of: measuring the pH of at least one of said pulpsuspension and said calcium-treated pulp suspension so as to therebymonitor the chemical reaction; and setting the pH of at least one ofsaid pulp suspension and said calcium-treated pulp suspension so as tothereby help control the chemical reaction, the pH thereof being setwithin a range of about 5.5 to 10.5.
 8. The process of claim 1, whereinsaid pulp suspension has an ash content, said ash content beingcontrollable within an approximate range of 1% to 70%.
 9. The process ofclaim 1, wherein said carbon-dioxide medium is introduced in a gaseousform.
 10. The process of claim 1, wherein said carbon-dioxide mediumbeing charged into said at least one reactor has a medium temperatureassociated therewith, said medium temperature being controlled within anapproximate range of −20° C. to 100° C.
 11. The process of claim 1,wherein brightness is used as an indicator for controlling the chemicalreaction.
 12. The process of claim 1, wherein said pulp suspension hasan ash content, said pulp suspension and said ash content each having apH associated therewith, the pH of at least one of said pulp suspensionand said ash content being used as a control parameter to at least oneof monitor and control the chemical reaction.
 13. The process of claim1, wherein said plurality of reactors includes partial reactors in whichpartial reactions of calcium-treated pulp suspension and saidcarbon-dioxide medium have occurred, said process including at least oneof the following steps:testing of partial reactions; switching on andoff of at least one partial reactor; and varying at least one operatingparameter of at least one partial reactor.
 14. The process of claim 1,wherein a pressure associated with each reactor is regulated in therange of about 0.1 bar to about 20 bar.
 15. The process of claim 1,wherein each said reactor has an energy input associated therewith, saidenergy input being in the approximate range of 0.1 kWh/t to 200 kWh/t.16. The process of claim 15, wherein said energy input is in theapproximate range of 0.5 kWh/t to 200 kWh/t.
 17. An apparatus forloading calcium carbonate into fibers contained in a pulp suspension viaa chemical reaction, said apparatus comprising: a source of a pulpsuspension, the pulp suspension including fibers therein, the pulpsuspension having at least one of calcium oxide and calcium hydroxideadded thereto; a source of a carbon-dioxide medium, the carbon-dioxidemedium being one of pure carbon dioxide and a medium containing carbondioxide; and a plurality of reactors, each reactor being configured forhaving the pulp suspension and the carbon-dioxide medium chargedthereinto and being further configured for promoting the chemicalreaction for loading calcium carbonate into the fibers.
 18. Theapparatus of claim 17, wherein said plurality of reactors includes atleast one section of reactors, said at least one section of reactorsbeing connected in series.
 19. The apparatus of claim 17, wherein saidplurality of reactors includes at least one section of reactors, said atleast one section of reactors being connected in parallel.
 20. Theapparatus of claim 17, wherein said plurality of reactors includes acombination of parallel-connected reactors and series-connectedreactors.